Conventionally, gas concentration measuring devices utilizing light have been used to measure various types of gas components of exhaust gas from a combustion system such as an internal combustion engine and an incinerator, and gas components of fuel gas to a gas system such as a gas engine and a fuel cell. Examples of known measurement methods using such a light-applying gas concentration measuring device include: Fourier-transform infrared spectroscopy (FTIR), which is a technique utilizing distribution of intensity of interfered infrared light; and tunable diode laser absorption spectroscopy (TDLAS), which is a technique utilizing absorption of applied laser light.
A TDLAS gas concentration measuring device is configured to measure concentration of a gas species of interest for measurement (“target gas”) by applying laser light having a wavelength corresponding to the absorption spectrum of the target gas and measuring the amount of attenuation of laser light transmitted through the gas (see Patent Literature 1 (PTL 1)). The TDLAS gas concentration measuring device is configured to eject purge gas such as instrument air and nitrogen gas to its measurement-purpose optical systems to prevent contamination of and condensation on the optical systems.